Even while interest in the viability of the A-B dimension as a hypothetical construct in differentiating successful from unsuccessful therapists continues unabated, it is unfortunately true that all of the burgeoning A-B research has been conducted with scales which are demonstrably far from optimum, even in the groups on which they were derived. In addition, existing scales have no validity whatsoever with respect to female psychotherapists. Preliminary analyses indicate that all existing A-B scales (including the Whitehorn-betz originals and their subsequent modifications) are based on faulty methodologies and incorporate possible errors in computation and analysis. Therefore, on the basis of the original data collected by Whitehorn, Betz, and their associates over a 16-year period at the Henry Phipps Psychiatric Clinic, the objective of this study is to derive an optimum A-B scale utilizing responses to the Strong Vocational Interest Blank. Methodological steps include: 1) separate analyses for male and female subjects; 2) elimination of cases in which the criterion may be unreliable; 3) orrection or purification of the criterion of therapist effectiveness through elimination (by multiple regression) of patient differences in potential and/or concurrent treatment; 4) use of split samples to cross-validate empirically selected items; 5) use of partial correlation to neutralize time-related effects; 6) maximization of internal consistency reliability while retaining criterion validity; 7) investigation of the optimum scale's reliability and factorial structure in new samples; and 8) demonstration of the optimum scale's superiority over existing scales.